Prenatal Depression and Infant Health: The Importance of Inadequately Measured, Unmeasured, and Unknown Confounds.

A recent study found that maternal antenatal depressive symptoms were associated with adverse infant general health outcomes and that gestational age, birth weight, and breastfeeding did not mediate the observed relationship. The authors suggested that antenatal depression can have a harmful effect on infant health through disturbed fetal programming driven by maternal symptoms and behaviors that influence the maternal and hence the fetal internal environment. The authors implied that interventions to diagnose and treat maternal depression can have a protective effect against disturbances in infant health. However, because of the observational nature of the study, cause-effect relationships cannot be conclusively stated. This is especially so because there were many confounds that the authors did not consider. The present article provides examples and explanations of how inadequately measured, unmeasured, and unknown confounds can explain observed relationships between explanatory and outcome variables, thereby negating cause-effect interpretations of study findings. It is important to minimize confounding when conducting observational studies, and this can only be done by comprehensively listing and efficiently measuring potential confounders in advance.